#include<bits/stdc++.h>
using namespace std;

int main(){
	float x1,y1,x2,y2;
	while(scanf("%f %f %f %f",&x1,&y1,&x2,&y2)!=EOF){
		printf("%.2f\n",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
	}
	return 0;
}
